Nitrate Poisoning in Livestock

Significant Stock Losses caused by Drought Feeding.
 
Deaths were caused by drought feeding of millet silage in one case and millet hay in the other. Approximately 10% of cattle died apparently overnight after being fed the millet products.
Laboratory tests confirmed that the cause was nitrate/nitrite poisoning in both cases.
Nitrates in fodder are converted to nitrites in the rumen. Nitrates in stored fodder can also be converted to nitrites when plant materials heat up or are attacked by bacteria or fungi. Normal levels of nitrite are converted to ammonia in the rumen by bacterial action. However excessive levels of nitrate or nitrite are poisonous.
 
Certain soil and environmental conditions facilitate nitrate uptake and accumulation by plants, eg.:
 
Use of nitrogen containing fertilizers
Low soil sulfur and molybdenum
Areas where stock have congregated and urinated and defecated (stock yards)
Drought
Cloudy or cold weather
Herbicide application, esp 2.4-D 
Wilting
Plant species
Stage of maturity of plant
Part of plant
 
Young plants have higher nitrate concentrations and most plant nitrate is located in the bottom third of the stalk.
Hays made from cereal crops, especially those grown under drought conditions and cut while "sappy" can develop toxic nitrite levels when they heat up.
Hays contain almost the same level of nitrate as the parent crop. Silage normally contains significantly less due to the fermentation process.
 
Sheep are less susceptible to nitrite poisoning than cattle, but can also be affected.
Stressed animals in poor health or poor condition are more susceptible and hungry animals are more likely to eat large amounts.
 
The risk of poisoning can be reduced by
Having feeds and forages analysed for nitrate levels.
Gradually introducing any new feeds by feeding small amounts frequently and diluting with known safe feeds.
Cattle can become acclimatized to relatively high levels of nitrate this way.
Frequent observation of stock, especially when changing food or grazing.
Don't overstock.
Prevent hungry stock from grazing on high risk fodder.
Do not graze high nitrate pastures for 7 days after rainfall, cloudy weather, frosts or high temperatures causing wilting.
Do not harvest pastures under these conditions either.
Graze these pastures during sunny afternoons above 15 degrees Celsius and remove livestock at night.
Never feed mouldy hay.
Harvest crops close to maturity and raise the cutter head selectively to avoid the bottom part of the stalk.
 
 Keep in mind that rapidly growing weeds after rainfall may also contain excessive levels of nitrate as well as cyanide (prussic acid).
 
 Keywords: cattle, sheep, fodder, drought, grazing, millet, nitrate, nitrite, 2.4 -D.